1. Field of the Invention
The present invention relates to a stack type optical disk changer, and more particularly to, a stack type optical disk changer which can prevent movement of a cartridge and each tray.
2. Description of the Background Art
In general, an optical disk changer charges a plurality of optical disks into each tray, so that the user can freely select and reproduce a target optical disk. The optical disk changer is classified into a rotary type optical disk changer and a stack type optical disk changer.
The stack type optical disk changer which can charge more optical disks than the rotary type optical disk changer has been recently popularly used.
FIG. 1 is a perspective view illustrating a conventional stack type optical disk changer, FIG. 2 is a plane view illustrating an operation of taking a cartridge out of a main frame in the conventional stack type optical disk changer, FIG. 3 is a plane view illustrating an operation of putting the cartridge into the main frame in the conventional stack type optical disk changer, and FIG. 4 is a front view illustrating the conventional stack type optical disk changer of FIG. 1.
Referring to FIGS. 1 to 4, in the conventional stack type optical disk changer 10, a cartridge 12 is installed to slide into or out of a main frame 11, and a plurality of trays 13a to 13e are sequentially slidably installed inside the cartridge 12.
An optical pick-up (not shown) is disposed at the inside rear portion of the main frame 11, and a tray loading unit 14 for loading one of the trays 13a to 13e selected by the user, for example, the tray 13c to the optical pick-up is disposed at the inside side portion of the main frame 11.
The tray loading unit 14 includes a plurality of tray loading gears 14b engaged with a cam 20 rotated by a driving unit 14a, for receiving power, and a tray loading lever 14c for loading the tray selected by the user, for example, the tray 13c to the optical pick-up by the tray loading gears 14b. 
A cartridge loading unit 15 for loading the cartridge 12 to the main frame 11 or unloading the cartridge 12 from the main frame 11 is disposed at the inside front portion of the main frame 11.
A cartridge loading gear 15a of the cartridge loading unit 15 is engaged with a rack 12a formed on the inner circumferential surface of the cartridge 12. Therefore, the cartridge 12 is loaded to the main frame 11 or unloaded from the main frame 11 according to the rotation direction of the cartridge loading gear 15a. 
In the conventional stack type optical disk changer 10, as shown in FIG. 2, when a driving unit 15b is driven in the forward direction to rotate the cartridge loading gear 15a in the anticlockwise direction, the cartridge 12 is slidably taken out of the main frame 11.
Conversely, as depicted in FIG. 3, when the driving unit 15b is driven in the backward direction to rotate the cartridge loading gear 15a in the clockwise direction, the cartridge 12 is slidably put into the main frame 11.
In the case that the cartridge 12 is put into the main frame 11, if the user selects an optical disk reproduction mode, the tray 13c selected by the user is loaded to the optical pick-up by the tray loading unit 14, and the optical pick-up reproduces an optical disk (not shown) positioned on the tray 13c. 
However, the conventional stack type optical disk changer 10 does not have a special device for preventing movement of the cartridge 12 in the reproduction mode or replacement mode of the optical disk. If external shaking or impact generated by transportation or sudden braking of a vehicle is applied to the optical disk changer 10, the cartridge 12 moves (shakes), to reduce quality of sound or image of the optical disk.
In addition, as shown in FIG. 4, the optical disk positioned on the tray 13d is separated from the tray 13d and damaged due to an interval d formed between the tray 13b and the tray 13d directly after the tray 13c is loaded to the optical disk, and even the optical disk changer 10 is mistakenly operated or gets out of order.